Generally, an image sensor is a semiconductor device that converts an optical image into an electric signal.
Recently, the CMOS image sensor has been spotlighted as the next generation image sensor.
A conventional CMOS image sensor includes a silicon substrate having a pixel region and a transistor region provided thereon with an interlayer dielectric layer including undoped silicon glass (USG), a bonding pad on the interlayer dielectric layer, and a protective layer on the interlayer dielectric layer having the bonding pad.
The CMOS image sensor manufactured in such a manner has many dangling bonds on a gate insulating layer and the silicon substrate. The dangling bonds degrade the performance of the image sensor.
In particular, when forming an isolation layer on the silicon substrate, many dangling bonds existing on the interface between the isolation layer and the silicon substrate may serve as a dark current source. Further, the dangling bonds generated when forming the gate insulating layer may reduce charge transfer efficiency because they may serve as a trap that captures electrons during transfer of photoelectrons.
Therefore, according to the manufacturing process of the CMOS image sensor, an annealing process is performed to remove defects such as dangling bonds and humidity.
An annealing process for the conventional CMOS image sensor is performed for a long time while applying the mixture of hydrogen gas and nitrogen gas at a normal pressure or at a pressure lower than the normal pressure, so the product yield may be lowered and device characteristics may be degraded.